1. Field of the Invention
The present invention relates to an apparatus and method for separating radioactive nuclides in a waste salt and recovering a refined salt from the waste salt, which are able to maximize process efficiency and operating efficiency of a process of regenerating a waste salt generated from a pyrochemical process of used nuclear fuel by converting radioactive nuclides in the waste salt into a thermally stable form and distilling the waste salt under a reduced pressure using a single apparatus having two top covers which are mountable for converting radioactive nuclides or distillation a waste salt, and highly improve applicability and utility in a remote operation facility for the waste salt treatment by further simplifying operation/handling compared with conventional processes.
2. Discussion of Related Art
Rare earth nuclides in a LiCl—KCl eutectic salt generated from a pyrochemical process of used nuclear fuel is converted into an insoluble compound and precipitated to the bottom of the eutectic salt, the eutectic salt containing the insoluble compound is divided into an upper refined salt and a precipitate layer, and rare earth nuclides and refined salt are recovered from the precipitate layer using technology of regenerating a LiCl—KCl eutectic waste salt, which was developed from a combination of an oxidative (or phosphorylative) precipitation process and a vacuum distillation process.
Such technology of regenerating a eutectic waste salt has been evaluated as world-leading technology in the process of disposing of a eutectic waste salt since it is used to separate at least 99% of the rare-earth nuclides and recover at least 95% of the eutectic salt.
However, such conventional technology of regenerating a eutectic waste salt is specifically divided into four processes: a chemical conversion and precipitation process, a process of separating a solid eutectic salt, a process of separating a precipitate layer, and a process of distilling a eutectic salt in a precipitate layer. Since the same number of apparatuses are required to perform the processes, operations of the apparatuses for performing the processes cause an increase in operating time and cost of equipment, which results in a decrease in operating efficiency.
Also, a process of separating a solid eutectic salt includes separating a solid salt in a reaction container, to which the eutectic salt in a solid state discharged after being subjected to a chemical conversion and precipitation process and being cooled at room temperature is stuck, by heating an outer wall of the reaction container using an electric heater in a state in which the reaction container is turned upside down. In this separation process, upper and lower portions of the solid salt are separated as a precipitate layer and a refined salt layer, respectively, in the reaction container. In such a process of separating a solid eutectic salt, the eutectic salt present in the precipitate layer may intermittently flow down and contaminate the lower refined salt layer. In this case, since it is difficult to separate the refined salt layer and the precipitate layer, the separated salt should often be repeatedly processed.
Meanwhile, since a refined salt layer and a precipitate layer including a rare-earth compound are separated by cutting the top of the precipitate layer using an electric cutter in the case of a process of separating a solid eutectic salt discharged in the process of separating a solid eutectic salt into a refined salt layer and a precipitate layer, fine salt particles may be scattered, and salt debris may be precipitated. Therefore, an additional apparatus for collecting and recovering these salts is required. Also, when the separated precipitate layer and refined salt layer are subjected to a process considering remote operations from facilities handling a radioactive material in a cylindrical shape, the precipitate layer and the refined salt layer may not be easily handled during a transfer process.
Also, the loss of salts may occur during the process of separating a solid eutectic salt and the process of separating a precipitate layer, thereby causing a decrease in salt recovery ratio. As the loss of salts is accumulated, the problems regarding operations of the apparatus and an increase in amount of waste to be further disposed may be caused.
Patent document: Korean Patent Publication No. 2012-0021568, Korean Registered Patent No. 0861262